The lead-acid battery is an electrochemical storage battery generally comprising a positive plate, a negative plate, and an electrolyte comprising aqueous sulfuric acid. The plates are held in a parallel orientation and electrically isolated by porous separators to allow free movement of charged ions. The positive battery plates contain a current collector (i.e., a metal plate or grid) covered with a layer of positive, electrically conductive lead dioxide (PbO2) on the surface. The negative battery plates contain a current collector covered with a negative, active material, which is typically lead (Pb) metal.
During discharge cycles, lead metal (Pb) supplied by the negative plate reacts with the ionized sulfuric acid electrolyte to form lead sulfate (PbSO4) on the surface of the negative plate, while the PbO2 located on the positive plate is converted into PbSO4 on or near the positive plate. During charging cycles (via an electron supply from an external electrical current), PbSO4 on the surface of the negative plate is converted back to Pb metal, and PbSO4 on the surface of the positive plate is converted back to PbO2. In effect, a charging cycle converts PbSO4 into Pb metal and PbO2; a discharge cycle releases the stored electrical potential by converting PbO2 and Pb metal back into PbSO4.
Lead-acid batteries are currently produced in flooded cell and valve regulated configurations. In flooded cell batteries, the electrodes/plates are immersed in electrolyte and gases created during charging are vented to the atmosphere. Valve regulated lead-acid batteries (VRLA) include a one-way valve which prevents external gases entering the battery but allows internal gases, such as oxygen generated during charging, to escape if internal pressure exceeds a certain threshold. In VRLA batteries, the electrolyte is normally immobilized either by absorption of the electrolyte into a glass mat separator or by gelling the sulfuric acid with silica particles.
Currently the negative plates of lead-acid batteries are produced by applying a paste of micron size lead oxide (PbO2) powder in sulfuric acid to electrically conducting lead alloy structures known as grids. Once the plates have been cured and dried, they can be assembled into a battery and charged to convert the PbO2 to Pb sponge. As indicated in, for example, U.S. Patent Application Publication No. 2009/0325068, it is normal to add an expander mixture to the lead oxide/sulfuric acid paste to improve the performance of the final negative electrode. The expander mixture typically comprises (a) barium sulfate to act as a nucleating agent for lead sulfate produced when the plate is discharged, (b) carbon to increase the electrical conductivity of the active material in the discharged state and (c) a lignosulfonate or other organic material to increase the surface area of the active material and to assist in stabilizing the physical structure of the active material.
U.S. Patent Application Publication No. 2004/0180264 discloses a lead-acid battery comprising an anode, a cathode and an electrolytic solution, wherein into the anode is added a carbon containing a simple substance and/or a compound, both having a catalysis for desulfurization or SOx oxidation. Suitable catalytic substances include Hf, Nb, Ta, W, Ag, Zn, Ni, Co, Mo, Cu, V, Mn, Ba, K, Cs, Rb, Sr and Na, or at least one oxide, sulfate, hydroxide or carbide thereof.
U.S. Patent Application Publication No. 2011/0020693 discloses an electrode for a lead acid battery comprising an electrode active material layer comprising a lead containing material, a porous carbon material and a binder, and a current collector, wherein when a weight of lead atom is A and a weight of porous carbon material is B, B/(A+B)×100 satisfies 1.0 to 90%; and said binder is a crystalline polymer having a melting temperature of 40° C. or less or is an amorphous polymer. The electrode active material layer comprises a layer including the lead containing material, and a layer including the porous carbon material and binder, wherein the latter is composed of spherical composite particles produced by spray drying.
U.S. Pat. No. 5,547,783 discloses a valve-regulated lead-acid battery in which the theoretical capacity (Ah) of the negative active material in the battery is less than that of the positive active material and the negative active material contains a conductive additive in the range of 0.5 weight % to 7.5 weight % of the negative active material. The conductive additive is carbon, acetylene black, polyaniline, tin powder, tin compound powder, etc. having an average particle diameter of 100μ or less.